Footwear

ABSTRACT

An improved article of footwear comprising a heelboard and an upper wherein the outer edge of the upper is bent around the heelboard and adhesively bonded to the lower surface thereof, wherein the improvement comprises a sheet of resin which covers at least a portion of the lower surface of the heelboard, said resin being selected from the group consisting of: A. copolymers of at least one olefin with at least one nonhydrocarbon aliphatic monomer, and B. blends of A with at least one polyolefin, whereby the adhesive bond between the upper and the heelboard is strengthened.

[ 1 Web. 2, 1972 [54] FUU'IIFWIEA 2,467,386 4/1949 Kamborian ..36/19.5 [72] Inventor: Donald Weight, chalfom St Gfles 2,909,854 10/1959 Edelstern ..36/44 UX gland OTHER PUBLlCATlONS [73] Assignee: Monsanto Chemicals Limited London EVA copolymers- Modern Plastics Encyclopedia- 1968- England pgs. 210- 213. [22] Filed: Apr. 3, 1970 Primary Examiner-Alfred R. Guest [2}] APPL 251555 Att0rneyJames L. Lewis, Richard W. Stemberg and James C. Logomasini [30] lForei A lication lPriorlt Data gm W y [57] STRACT Apr. 25, 1969 Great Britain ..21,332/69 An improved article of footwear comprising a heelboard and [52] US. Cl ..36/44 an pp wherein the Outer g of the pp is bent around [51] 1111.131. ..A43b 13/38 the heelboard n h ively bonded to the lower surface [58] Field 01 Search ..36/44, 19.5; 161/164, 252 thereof, wherein the improvement comprises a sheet of resin which covers at least a portion of the lower surface of the heel- [56] References Cited board, said resin being selected from the group consisting of:

Ar copolymer of at least one olefin with at least one non- UNITED STATES PATENTS hydrocarbon aliphatic monomer, and 2,101,693 12/1937 Taraci ..36/l9.5 blends of A with at least one 'Y whereby the 3,449,844 6/1969 Spence 36/44 adhesive bond between the upper and the heelboard is 1,701,896 2/1929 Richard ...36/19.5 X Strengthened- 3,342,902 9/1967 Peterkin... .....161/252 X 18 Cl 2D 3,431,163 3/1969 o11b6n..... ..161/164 x 2,287,643 6/1942 Ruggiero ..36/19.5

Prmmrm 22 m2 3. 6 3 1 3 5 3 Invenlor DOW/LID ()JEIG HT A llorney FOOTWEAR This invention relates to footwear, and particularly to an article of outer footwear such as a boot or shoe.

Articles of outer footwear such as a boot or shoe normally comprise an insole assembly of a flexible forepart and a relatively stiff heelboard, the edge of the upper being turned underneath the insole assembly and fixed thereto by suitable means. The heel and the sole proper are then fixed to the lower side of the insole assembly in a subsequent operation. Very often the heelboard is of cellulosic or other fibers bonded together by an adhesive such as a styrene-butadiene or other resin, while the flexible forepart can be of, for example, leather or preferably a foamed resin as described in British Pat. No. 1,198,552 (U.S. Pat. application Ser. No. 793,559, filed Jan. 23, 1969).

The method employed for fixing the downturned edge of the upper to the insole assembly is of vital importance, since a failure here results in almost irreparable damage to the whole boot or shoe. Adhesives can be employed at the forepart, but it has always been necessary to use nails at the heelboard, attempts to use adhesives here having failed, In particular, failures have occurred as a result of delamination of the bonded fiber used for the heelboard, and it is therefore still necessary to employ nails at this end of the shoe even when an adhesive is employed at the forepart. Nails rust and in time lose their hold, and it would be very desirable to eliminate the necessity for this nailing operation.

It has now been found that a good adhesive bond can be effected if the lower surface of the heelboard comprises a sheet of resin, the resin being a copolymer of an olefin and a nonhydrocarbon aliphatic monomer or a blend of such a copolymer with a polyolefin.

Accordingly, the invention comprises an article of footwear, such as a boot or shoe, having a heelboard and an upper, the outer edge of the upper being bent round the heelboard and adhesively bonded to the lower surface thereof, in which the lower surface of the heelboard comprises a sheet of resin, the resin being a copolymer of at least one olefin and at least one nonhydrocarbon aliphatic monomer or a blend of such a copolymer with at least one polyolefin, so as to improve the strength of the adhesive bond.

Also part ofthe invention is aheelboard having a lower surface as defined above.

Preferably, the resin sheet extends completely over the lower surface of the heelboard, and preferably also it is integral with a flexible forepart so as to form an insole assembly.

In the copolymer the olefin component is preferably an olefin having from two to four carbons such as for example ethylene, propylene, butylene, isobutylene or a mixture of such olefins. The most preferred olefin is, however, ethylene. The nonhydrocarbon component of the copolymer can for example be an alkenyl halide, for example, vinyl chloride or allyl chloride, an unsaturated alcohol such as for example allyl alcohol or the notional vinyl alcohol, or an amide such as for instance acrylamide, but preferably the nonhydrocarbon monomer is an unsaturated ester. An unsaturated ester can be the result of the reaction of an unsaturated alcohol with a saturated acid, of a saturated alcohol with an unsaturated acid or of an unsaturated alcohol with an unsaturated acid so that suitable esters include for example vinyl acetate, ethyl acrylate and allyl methacrylate. Preferred unsaturated esters, however, are those formed from a lower unsaturated alcohol and a lower aliphatic carboxylic acid. The unsaturated alcohol portion ofsuch an acid comonomer can for instance contain up to four carbon atoms such as, for example, allyl alcohol or a methallyl alcohol but preferably the alcohol is the notional vinyl alcohol. The acid portion of the molecule can also for instance contain up to four carbon atoms for example it can be acetic, propionic, or a butyric acid; acetic acid is, however preferred. There can if desired be more than two monomers in the copolymer; for example the olefin can in fact be a mixture of two or more hydrocarbons, so that the copolymer can be, for example, a mixture of ethylene and propylene copolymerized with vinyl acetate; or there can be a mixture of two or more nonhydrocarbon monomers, for example, the copolymer can be one of ethylene with a mixture of ethyl acrylate and methyl methacrylate or with a mixture of vinyl acetate and vinyl alcohol. The last-named copolymer can be conveniently produced by the partial hydrolysis of a copolymer of ethylene and vinyl acetate. The illustrations show:

FIG. 1 a perspective view of an insole heelboard according to the invention, and

FIG. 2 a section through a shoe incorporating the insole assembly shown in FIG. 1.

The insole assembly consists of a heelboard (1) and a flexi' ble forepart (2), the flexible forepart and the lower surface of the heelboard being composed of a sheet of foamed resin. In addition the heelboard (1) comprises .a shank board (3), for example of cellulose fiber, skived to zero thickness at its forward end (4) and adhered to the upper surface of the sheet of foamed resin.

The shoe illustrated in FIG. 2 comprises an insole assembly (5) having a heelboard (6), the lower surface (7) of which is composed of a sheet of foamed resin which forms the forepart (8). I

In constructing the shoe the outer edge (9) of the upper (10) is bent around the heelboard (6) and adhesively bonded to its lower surface (7 The sole proper (11) is then adhesively attached to the insole assembly (5) followed by the heel (12).

The resin preferably contains from about 2 to about 17 percent by weight of the nonhydrocarbon monomer, more preferably from about 3 to about 15 percent by weight and for example from about 3 to about 5 or from about 10 to about 13 percent by weight. Excellent results have been obtained em ploying resins containing respectively about 4 percent and about 12 percent of the nonhydrocarbon monomer. Preferably the resin comprises a copolymer of the olefin and the nonhydrocarbon monomer, but it can be a blend of such a copolymer with a polyolefin, and in this: event, of course, the proportion of nonhydrocarbon monomer in the copolymer can be greater than about 17 percent by weight, for instance up to about 30 percent or about 45 percent by weight, sufficient polyolefin being blended with the copolymer to reduce the amount of nonhydrocarbon monomer in the resin as a whole to the value desired. Where the resin is a blend, the polyolefin can be of the low-pressure" type, for example a polyethylene or polypropylene made using a chromium oxide or organometallic catalyst system but preferably it is a highpressure polyethylene, for instance having a density from about 0.90 to 0.94 grams per cc.

The copolymer can itself be a blend of two copolymers of an olefinic hydrocarbon and nonhydrocarbon monomer.

Preferably the sheet has a substantially uniform thickness, by which it is meant that the thickness does not vary by more than about 15 percent, and preferably any thickness variations are not greater than about 5 percent. Where, as is preferred, the sheet is integral with the insole flexible forepart, the thickness is conveniently determined by requirements of this part of the sheet. In general, the type of footwear being made determines the choice of insole thickness, thinner insoles normally being needed for children's and ladies shoes than for mens boots or shoes. Preferably the thickness is from about 0.05 to 0.1 or 0.15 inch, and very often from about 0.06 to about 0.085 inch is particularly suitable.

According to an important preferred feature of the invention, the resin sheet is foamed. Preferably the foam has a substantially closed cell structure, by which it is meant that the majority, normally at least percent, of the cells are closed. Preferably the majority of the cells, more preferably at least 75 percent, of the cells have a diameter from 0.004 to 0.04 inch, for example from 0.01 to 0.03 inch. The density of the foamed sheet is very often from 20 to 40 pounds per cubic foot, a density at the at lower end of this range, for example about 24 pounds per cubic foot, being usually most suitable, The foamed sheet may have a nonfoamed skin on each side, but this is not usually thicker than about 0.002 inch.

assembly having a The sheet is preferably an extruded one. A nonfoamed sheet can be made by conventional methods, while a foamed sheet is normally made by extruding a foamable mixture of the resin and a suitable blowing agent under pressure through a die into a zone of lower pressure (usually the atmosphere) so that the expansion of the blowing agent and foaming of the resin takes place. Normally a slit die is used, although it is perfectly possible to employ an annular die to extrude a tube of resin that is later slit longitudinally and opened out into a flat sheet. Where a slit die is used to produce a foamed sheet, the die can have a flared outlet if desired and a a pair of rollers can be placed in front of it so that the extruding sheet passes between them; such rollers have been found to assist in the production of a smooth flat sheet free of thickness variations and corrugations. Alternatively, the use of a single roller, as described in U.S. Pat. application Ser. No. 27,973 filed Apr. 13, 1970, gives very good results.

U.S. Pat. application Ser. No. 27,973 filed Apr. 13, 1970 describes a process for producing a flat sheet ofa foamed thermoplastic synthetic resin, which comprises extruding a layer of a foamable thermoplastic synthetic resin through a slit die orifice into contact with the cylindrical surface of a single roller rotatable about an axis parallel to the slit, such that the layer foamed while it is in contact with the rotating roller surface and expansion in a direction parallel to the slit is substantially limited by such contact, and withdrawing the resulting foamed sheet from the roller.

The resin employed in producing a foamed sheet is of course foamable, and this means that it is in admixture with a blowing agent which is preferably a gas or vapor under normally atmospheric conditions but which can be a volatile liquid. In many cases the blowing agent is one that is normally gaseous but which while under pressure before extrusion will be present in solution in the molten or semimolten resin. Examples of volatile substances than can be used include lower aliphatic hydrocarbons such as ethane, propane, butane or pentane, lower alkyl halides such as methyl chloride, tricholomethane or l,2-dichlorotetrafluoroethane, and inorganic gases such as carbon dioxide or nitrogen. Nitrogen and the low aliphatic hydrocarbons, especially butane or isobutylene, are preferred, and a mixture of nitrogen and a low aliphatic hydrocarbon is often particularly useful. The blowing agent can also be a chemical blowing agent, which can for example be a bicarbonate such as, for example, sodium bicarbonate or ammonium bicarbonate, or an organic nitrogen compound that yields nitrogen on heating, such as for example dinitrosopentamethylediamine or barium azodicarboxylate. From 3 to 30 percent especially from 7 to 20 percent by weight based on the weight of the resin is often a suitable proportion ofa liquid or readily liquefiable blowing agent. Where the blowing agent is a permanent gas it is more convenient to consider relative volumes at Standard Temperature and Pressure, and for example the use of0.5 to parts, preferably from 1 to 2 parts by volume of nitrogen at S.T.P. in conjunction with 1 part by volume of polyethylene has given excellent results. Often the use of amounts of blowing agent at the lower end of the above ranges results in the production of a thicker sheet.

Sometimes the blowing agent is employed in conjunction with a nucleating agent, which assists in the formation of a large number of fine cells. A wide range of nucleating agents can be employed, including finely divided inert solids such as for example silica or alumina (if desired in conjunction with zinc stearate), or small quantities or a substance that decomposes at the extrusion temperature to give a gas can be used. An example of the latter class of nucleating agents is sodium bicarbonate, if desired in conjunction with a weak acid such as for example tartaric or citric acid. Boric acid, calcium acetate, calcium propionate and calcium benzoate are each excellent nucleating agents. A small proportion of the nucleating agent, for example up to 5 percent by weight of the resin, is usually effective.

The resin can also contain such additives as coloring agents, antioxidants, stabilizers, lubricants and so on if desired. For

example it is often desirable to color the resin where it is to form part of a sandal, the construction of which renders the edge of the insole assembly visible as the welt. A clay or other brown pigment is very often suitable for this purpose.

According to a preferred feature of the invention, the resin sheet is subjectedto the action of an electric discharge. This has been found not only to improve the adhesion of hot melt and other adhesives to the sheet, but also surprisingly to reduce undesirable adhesion of the insole to any metal platen or press foot employed in assembling the shoe. A voltage, preferably alternating, above 3,000 volts, preferable from 5,000 to 30,000 volts, is usually suitable, especially one having a frequency from 1,000 to 100,000 cycles per second. Preferably it is a corona discharge, but it can be a spark or spray discharge. Preferably both sides of the sheet are treated, with the electrodes situated for example from 0.005 to 0.2 inch away from the surfaces, and an application time from 0.003 to I second, especially from 0.01 to 0.5 second, is generally satisfactory.

The resin sheet is preferably bonded to the heelboard by means of an adhesive, for example a cold or hot-melt adhesive. Specific examples of suitable adhesives include polyvinyl acetate, polyurethane and neoprene, adhesives as well as hotmelt adhesives of the polyester or polyamide type. Alternatively, heat-sealing can be employed.

The production of the articles of footwear can follow normalpractice, except for the use of an adhesive at the heel end instead of nails, although it is necessary where the resin sheet is foamed to ensure that the degree of exposure to elevated temperatures, for instance when using a hot-melt adhesive, is not sufficient to cause collapse of the foam structure, This can generally be arranged where the necessary bonding between the sheet and other components of the shoe is achieved by means ofa cold or hot-melt adhesive or with a polyurethane or neoprene adhesive, or even by injection molding of a plasticized polyvinyl chloride sole and heel, provided that contact with elevated temperatures is maintained for as short a time as possible. It is for instance surprising that a polyamide or polyester hot-melt adhesive can be used at 240 C. with a resin having a softening temperature of only C. or even less, if the period of time for which the insole is exposed to this temperature is not more than 5 seconds. Even better results in this respect can be obtained if the resin contains a relatively small proportion of nonhydrocarbon monomer, for example from 3 to 7 percent or 3 to 5 percent, by weight. Any metal platen or press foot maintained in contact with the insole during the process should normally be at a temperature lower than the softening point of the resin. Rubber vulcanizing is not in general a suitable method, owing to the excessive temperature/time cycles involved. Traditional methods such as stitching or nailing can, of course, be employed, for example for fixing the sole and heel, but this in not preferred since full benefit from the advantages of the invention is not thereby achieved.

The material of the heelboard itself is not of great importance, any conventionally used material such as for instance cardboard or a resin-bonded cellulosic fiber board being normally suitable. However, it should be remembered that the invention may permit the employment of a somewhat cheaper material than would otherwise be possible.

Where, as is preferred, the resin sheet is integral with the flexible forepart of the insole assembly, the resulting excellent flexibility of the insole assemblies renders them particularly useful as components of ladies casual shoes and childrens footwear, but they can also be very well employed in, for example, mens shoes or boots, ladies court shoes, ladies fashion boots or sports footwear for either sex.

The invention is illustrated by the following Examples.

EXAMPLE I This example describes a shoe according to the invention.

A sheet of foamed resin was first produced from a copolymer ofethylene and vinyl acetate containing 12 percent by weight of vinyl acetate. Ninety-eight pounds of the resin in the form of granules were dry blended with 2 pounds of anhydrous calcium acetate to act as nucleating agent. The resulting mixture was fed into the hopper ofa screw extruder having a barrel of nominal diameter 1 /2 inches, nitrogen under pressure was injected into the molten mixture in the extruder barrel and the resulting foamable composition was extruded at a temperature of 130 C. into the atmosphere through a slit die 6 inches long and 0.025 inch wide. The product was a soft foam strip 0.08 inch thick, of density 24 pounds per cubic foot and having a fine closed cell structure.

Both sides of the sheet were subjected to the action of an alternating electric discharge of 10,000 volts and 3 kilocycles per second, by passing the sheet between two electrodes spaced 0.15 inch apart, each part of the sheet being exposed to the discharge for one tenth ofa second.

The sheet was cut into pieces in the shape ofthrough insoles (that is to say extending over both sole and heel) suitable for ladies casual shoes, and each insole was then adhered under pressure to a heelboard, made of a cellulose fiber board known as shank board," by means of a neoprene adhesive at 70 C. for 5 seconds. The heelboard has a thickness of /8 inch skived to zero at its forward end, and the foamed resin sheet extended over its entire lower surface. A leather upper was lasted to the insole assembly (including the heel) by means of neoprene adhesive and finally a rubber composition sole and heel were attached to the insole and heelboard, also by neoprene adhesive. No nails were employed at any stage.

The resulting shoe was found to be strong and comfortable, and survived extended wearer trails without failure of the adhesive bond between the upper and the heelboard. The peeling strength of the bond was 19 pounds weight per inch in one direction and 17 /2 pounds weight per inch at right angles to the first direction. in contrast, early failure occurred at the heel bond in a shoe similarly constructed but having the upper bonded directly to the shank board. The peeling strengths of the bond at the heel of the latter shoe were only 4.25 and 2.5 pounds weight per inch respectively in the two directions.

EXAMPLE II This example describes another shoe according to the invention, the proportion of polymerized vinyl acetate in the resin ofthe insole being lower than in the previous example.

The operations described in the previous example were repeated except that the proportion of polymerized vinyl acetate in the resin was 4 percent by weight. Neoprene adhesive was used as before in bonding the foamed resin sheet to the shank board, but all the other bonding operations were effected by means of a polyamide hot-melt adhesive. The resulting shoe was found to be similarly strong and comfortable, and wearer trials were just as successful as those described previously, but the insole possessed the additional advantage of reduced sensitivity to the effects of heat during application of the neoprene adhesive, thus permitting the use of slightly more severe bonding conditions if required. The peeling strengths of the bonding at the heel in two directions at right angles to each other were respectively 9 and l 1 pounds weight per inch.

What is claimed is:

l. In an article of footwear comprising a heelboard and an upper wherein the outer edge of the upper is bent around the heelboard and adhesively bonded to the lower surface thereof, the improvement which comprises a sheet of resin which covers at least a portion of the lower surface of the heelboard, said resin being selected from the group consisting of:

A. copolymers of at least one olefin with at least one nonhydrocarbon aliphatic monomer, said nonhydrocarbon aliphatic monomer or monomers comprising about 3 to about 15 percent by weight ofsaid copolymer; and

B. blends ofA with at least one polyolefin, whereby the adhesive bond between the upper and the heelboard is strengthened. I 2. An article of footwear according to claim 1, in which the resin sheet extends completely over the lower surface of the heelboard.

3. An article of footwear according to claim 1 in which the resin sheet is integral with a flexible forepart so as to form an insole assembly.

ll. An article of footwear according to claim l in which in the copolymer the olefin component is an olefin having from two to four carbon atoms.

5. An article of footwear according to claim 4, in which the olefin is ethylene.

6. An article of footwear according to claim 1 in which the nonhydrocarbon component is an unsaturated ester.

'7. An article of footwear according to claim 6, in which the ester is an ester of a lower unsaturated alcohol with a lower aliphatic carboxylic acid.

fl. An article of footwear according to claim 7, in which the ester is vinyl acetate.

9. An article of footwear according to claim 1 in which the copolymer contains from about 3 to about 15 percent by weight of the nonhydrocarbon monomer.

110. An article offootwear according to claim 9, in which the resin contains from about 3 to about 5 percent by weight of the nonhydrocarbon monomer.

llll. An article of footwear according to claim 1, in which the resin sheet has a substantially uniform thickness of from about 0.06 to about 0.085 inch.

112. An article of footwear according to claim I, in which the resin sheet is foamed.

13. An article of footwear according to claim l2, in which the foamed resin has a substantially closed structure and the majority of the cells have a diameter from 0.004 inch to 0.04 inch.

ll l. An article of footwear according to claim 13, in which the density of the foamed resin is from 22 to 30 pounds per cubic foot.

15. An article of footwear according to claim 1, resin sheet is one that has been subjected to the electric discharge.

16. An article offootwear according to claim 1, in which the adhesive bond between the outer edge of the upper and the resin sheet is achieved by means of an adhesive selected from the group consisting of cold adhesives, hotmelt adhesives, polyurethane adhesives and neoprene adhesivesv l7. An article of footwear according to claim 1, in which during the course of the bonding the resin sheet has been exposed to an elevated temperature for a period of time not in excess of 5 seconds.

18. A heelboard for use in constructing an article of outer footwear such as a boot or shoe, comprising a cellulose fiber board having a lower surface that comprises a sheet of resin, the resin being a copolymer of an olefin and a nonhydrocarbon aliphatic monomer or a blend of such a copolymer with a polyolefin.

in which the action of an 

2. An article of footwear according to claim 1, in which the resin sheet extends completely over the lower surface of the heelboard.
 3. An article of footwear according to claim 1 in which the resin sheet is integral with a flexible forepart so as to form an insole assembly.
 4. An article of footwear according to claim 1 in which in the copolymer the olefin component is an olefin having from two to four carbon atoms.
 5. An article of footwear according to claim 4, in which the olefin is ethylene.
 6. An article of footwear according to claim 1 in which the nonhydrocarbon component is an unsaturated ester.
 7. An article of footwear according to claim 6, in which the ester is an ester of a lower unsaturated alcohol with a lower aliphatic carboxylic acid.
 8. An article of footwear according to claim 7, in which the ester is vinyl acetate.
 9. An article of footwear according to claim 1 in which The copolymer contains from about 3 to about 15 percent by weight of the nonhydrocarbon monomer.
 10. An article of footwear according to claim 9, in which the resin contains from about 3 to about 5 percent by weight of the nonhydrocarbon monomer.
 11. An article of footwear according to claim 1, in which the resin sheet has a substantially uniform thickness of from about 0.06 to about 0.085 inch.
 12. An article of footwear according to claim 1, in which the resin sheet is foamed.
 13. An article of footwear according to claim 12, in which the foamed resin has a substantially closed structure and the majority of the cells have a diameter from 0.004 inch to 0.04 inch.
 14. An article of footwear according to claim 13, in which the density of the foamed resin is from 22 to 30 pounds per cubic foot.
 15. An article of footwear according to claim 1, in which the resin sheet is one that has been subjected to the action of an electric discharge.
 16. An article of footwear according to claim 1, in which the adhesive bond between the outer edge of the upper and the resin sheet is achieved by means of an adhesive selected from the group consisting of cold adhesives, hot-melt adhesives, polyurethane adhesives and neoprene adhesives.
 17. An article of footwear according to claim 1, in which during the course of the bonding the resin sheet has been exposed to an elevated temperature for a period of time not in excess of 5 seconds.
 18. A heelboard for use in constructing an article of outer footwear such as a boot or shoe, comprising a cellulose fiber board having a lower surface that comprises a sheet of resin, the resin being a copolymer of an olefin and a nonhydrocarbon aliphatic monomer or a blend of such a copolymer with a polyolefin. 